1. Technical Field
The invention relates to a lens assembly equipped with a lens for forming an image using subject light on an imaging device and to an imaging apparatus having the lens assembly.
2. Description of the Related Art
Recently, cameras become mounted in vehicles. Cameras provided in vehicles are used as surveillance cameras or as driving-assistance cameras. Since display screens have been provided on driver's seats as navigation systems have become popular, the latter case is intended to display an image taken by the camera on the display screen.
In such on-board cameras, most of those are required to have waterproof performance since those are mainly used outside of vehicles. In order to achieve sufficient waterproof performance without an increase in camera size in accordance with the requirement, it has been attempted to provide, in the on-board cameras, small-sized lens assemblies excellent in waterproof performance.
FIG. 5 is a view illustrating a section of a related-art lens assembly taken along an optical axis of a taking lens.
FIG. 5 shows a lens assembly 100 including a taking lens 101_1 of a first group, a taking lens 101_2 of a second group, a taking lens 101_3 of a third group, and a taking lens 101_4 of a fourth group in order from an incident side of subject light A. Furthermore, FIG. 5 shows a lens frame 102 housing these taking lenses 101_1, 101_2, 101_3, and 101_4 and an O-ring 103 disposed between a periphery of the taking lens 101_1 and an inner surface of the lens frame 102. Examples of a material of the O-ring 103 include an ethylene propylene based rubber, a silicon rubber, and the like.
Specifically, a groove 101_1a is provided on the periphery of the taking lens 101_1, and the O-ring 103 is fitted into the groove 101_1a. The O-ring 103 is disposed with being pressed by the inner surface, corresponding to the groove 101_1a, of the lens frame 102. The O-ring 103 is a rubber member which is adapted to exhibit waterproof performance after the taking lens 101_1 is housed in the lens frame 102. Furthermore, the lens assembly 100 actually includes a lens holder which is attached to the lens frame 102 and in which an imaging device is disposed. However, the lens holder is not shown in the figure.
Also, JP 2002-90603 A (corresponding to U.S. Pat. No. 6,507,700) has proposed a lens assembly in which a protrusion of a leading end of the lens frame is caulked on the front surface side of the taking lens in the way of thermal adhesion in a state where the O-ring disposed between the periphery of the taking lens and the inner surface of the lens frame is pressed, thereby securing waterproof performance between the taking lens and the lens frame.
In the related-art lens assembly shown in FIG. 5, the O-ring, which is fitted into the groove provided on the periphery of the taking lens, is pressed by the inner surface of the lens frame, thereby securing waterproof performance between the taking lens and the lens frame. Also, in the lens assembly described in JP 2002-90603 A, the protrusion of the leading end of the lens frame is caulked on the front surface side of the taking lens in the way of thermal adhesion in the state where the O-ring disposed between the periphery of the taking lens and the inner surface of the lens frame is pressed, thereby securing waterproof performance between the taking lens and the lens frame. As described above, in order to secure waterproof performance, the related-art lens assembly is configured so that the O-ring is pressed between the periphery of the taking lens and the inner surface of the lens frame.
However, in such a configuration, waterproof performance greatly depends on a mounting strength between the taking lens and the lens frame, which press the O-ring. Here, if variation occurs in mounting strength between the taking lens and the lens frame in the assembling process of the lens assembly, a problem arises in that variation occurs in waterproof performance. Furthermore, when the lens assembly is mounted on an on-board camera, if dimensions of the taking lens and the lens frame are varied with time, due to change of environmental conditions such as humidity and temperature, or the like, sometimes the mounting strength between the taking lens and the lens frame may deteriorate. In such a case, a problem arises in that waterproof performance deteriorates. Accordingly, the related-art lens assembly has a problem of low waterproof performance.